1. Field of the Invention
The invention relates to a manufacturing method of an electrode and wet granules.
2. Description of Related Art
A non-aqueous electrolyte secondary battery such as a lithium-ion secondary battery is used in a hybrid vehicle (HV), a plug-in hybrid vehicle (PHV), an electric vehicle (EV), or the like. The non-aqueous electrolyte secondary battery includes a positive electrode and a negative electrode, which form a pair of electrodes, a separator which insulates the electrodes from each other, and a non-aqueous electrolyte. As the structure of the electrode (the positive electrode or the negative electrode) for the non-aqueous electrolyte secondary battery, a structure including a current collector formed of a metal foil or the like, and an electrode layer (electrode active material layer) which is formed thereon and contains an electrode active material is known.
In Japanese Patent Application Publication No. 2002-110145 (JP 2002-110145 A), a non-aqueous electrolyte secondary battery having a positive electrode plate in which a positive electrode mixture containing a positive electrode active material, a conductive material, and a binding material is applied onto a current collector and dried is disclosed. Here, after dry-mixing the positive electrode active material and the conductive material, an organic solvent is added thereto to be wet-dispersed. Furthermore, a dispersed binding material solution is added to the organic solvent and the resultant is kneaded, thereby manufacturing the positive electrode mixture.
However, there is known a manufacturing method of an electrode in which wet granules (for example, corresponding to the positive electrode mixture of JP 2002-110145 A) are supplied between a first roll and a second roll which rotate in opposite directions to each other, and the wet granules are allowed to adhere to the first roll while being rolled, thereby forming an electrode material layer. By drying the electrode material layer, an electrode layer is formed. A method of transporting the current collector is not particularly limited. For example, the electrode material layer may also be formed on the current collector while transporting the current collector using the first roll or the second roll. Otherwise, by transporting the current collector using a third roll that rotates reversely to the first roll, the electrode material layer adhered to the first roll may be transferred onto the current collector on the third roll.
The inventors found the following possibility regarding a manufacturing method of an electrode in which an electrode material layer is formed by rolling the wet granules described above. In a case of manufacturing wet granules according to the method of the related art disclosed in JP 2002-110145 A, since stirring is performed at a high speed for a long period of time during the kneading process, the wet granules are consolidated. Therefore, the malleability of the wet granules during rolling is degraded, and pinholes may be generated in the formed electrode material layer.
On the contrary, when stirring is performed at a low speed in the kneading process, the particle size of the wet granules becomes coarsened. Therefore, there is concern that coarse granules are caught on the rolls during rolling, and streaks may be generated in the electrode material layer. That is, there is a possibility that the wet granules according to the related art may cause the degradation in the film-forming properties of the electrode material layer formed by rolling.